1. Technical Field
The present invention relates to a piezoelectric element, a method for manufacturing the same, and a piezoelectric element-applied device.
2. Related Art
Heretofore, various piezoelectric element-applied devices employing a piezoelectric element for the electromechanical conversion mechanism of a Micro Electro Mechanical System (MEMS) element have been reported. In the piezoelectric element-applied devices, a MEMS actuator, a MEMS sensor, and the like are mounted as the MEMS element. For example, in a liquid ejecting head typified by an ink jet recording head, a pressure generating chamber communicating with a nozzle opening is partially configured from a diaphragm and also the MEMS actuator is configured by providing a piezoelectric element in the diaphragm. Ink in the pressure generating chamber is pressurized by deforming the diaphragm by voltage application to the MEMS actuator, whereby ink droplets are discharged from the nozzle opening.
As a piezoelectric layer configuring this kind of piezoelectric element, a piezoelectric layer containing lead zirconate titanate (PZT) (Japanese Patent Laid-Open No. 2001-223404) is mentioned. In addition thereto, there is a circumstance in which a piezoelectric layer capable of improving the piezoelectric characteristics has been researched in response to recent demands for a further size reduction, higher performance, and the like of the MEMS element.
For example, a piezoelectric layer has been proposed which contains a single crystal (Pb(Mg1/3, Nb2/3)O3—PbTiO3: PMN-PT) which contains a composite oxide of perovskite type oxides represented by General Formula ABO3 and in which lead magnesium niobate and lead titanate form a solid solution (Japanese Patent Laid-Open No. 2007-088441). The PMN-PT is known to show high electromechanical coupling coefficient, piezoelectric constant, and specific dielectric constant (T. Ogawa, Jpn. J. Appl. Phys., 47, 7655-7658 (2008)). Thus, an improvement of the piezoelectric characteristics is expected by obtaining a piezoelectric layer using such PMN-PT. However, the PMN-PT has been pointed out to have a possibility that Mg having a small atomic number is segregated on the interface between the piezoelectric layer and a lower electrode or diffuses into the lower electrode to reach the diaphragm in the lower electrode in a baking process which is one of the formation processes of the piezoelectric layer. When Mg is segregated on the interface between the piezoelectric layer and the lower electrode, a good interface cannot be formed, and thus the insulation properties and the breakdown voltage decrease, which leads to a reduction in reliability. Moreover, when Mg reaches the diaphragm, the Mg reacts with constituent materials (for example, Si) of the diaphragm on the interface between the lower electrode and the diaphragm to cause shape defects and the like, which may lead to a reduction in reliability.
From the viewpoint of preventing such defects, it has been proposed to provide a titanium oxide layer and a bismuth containing layer between a first electrode and a diaphragm under a piezoelectric layer containing Bi, although the diffusing metal types are different (Japanese Patent Laid-Open No. 2011-189586). Japanese Patent Laid-Open No. 2011-189586 describes that the titanium oxide layer and the bismuth containing layer serve as a stopper and can prevent further diffusion of Bi passing through the first electrode into the diaphragm.
However, when the titanium oxide layer described in Japanese Patent Laid-Open No. 2011-189586 is provided as a stopper layer against Mg contained in the PMN-PT between the first electrode and the diaphragm, the diffusing Mg and the titanium oxide react with other, which may cause a reduction in adhesiveness between the first electrode and the diaphragm and shape defects.
When a configuration of suppressing the diffusion of the Mg by the first electrode is employed, the piezoelectric layer and the first electrode cannot form a good interface, and thus the insulation properties and the breakdown voltage decrease, which may lead to a reduction in reliability.
As described above, with the former technique, it has been difficult to secure high reliability using a material (for example, PMN-PT) useful for an improvement of the piezoelectric characteristics. Such problems similarly arise in the case of piezoelectric elements including piezoelectric materials containing Mg, without being limited to the case where the PMN-PT is used. Moreover, the problems similarly arise also in other piezoelectric element-applied devices carrying the MEMS actuator, the MEMS sensor, and the like employing such a piezoelectric element, without being limited to the liquid ejecting head.